(1) Field of the Invention
The present invention relates to the field of disk drive technology. Specifically the present invention relates to design of outer arms of actuator assemblies of hard disk drives.
(2) Prior Art
Disk drive storage mediums, or "hard" disk drives, are mechanisms that store digital information on a spinning disk ("disc") or platter. The metallic platters are approximately from 3 inches in diameter up to 8 inches or more depending on the type of disk drive used or the storage capacity of the drive. Several platters arranged in parallel, one mounted on top of the next, rest in a drive case. Each platter is centrally fixed and carefully aligned in order to provide the spinning action required. A platter has two sides in which information can be stored. Also mounted to the drive case is an actuator arm which holds a read/write head associated with each platter side. If there are eight platters there could be up to 16 heads attached to the actuator arm.
The actuator arm assembly remains fixed with respect to the spinning platters but can move across the radius (position A to B) of the spinning platter in order to provide access to all of the surface area of the platter as the platter spins and as the actuator arm moves the read/write head across the platter diameter. Since the read/write head 22 remains in a fixed path and the platters spin, data is stored according to the arc of the heads across the platters, this is a circle. Therefore, magnetic data stored on a hard drive platter is stored in circular paths or sectors by the magnetic head passing across the magnetic surface. The rate that this information can be accessed or stored depends on the rate that the platters can spin. Conventional prior art disk drives can obtain a spin rate of approximately 3600 to 6400 revolutions per minute. The faster the spin rate, the faster information can be supplied by the drive and stored to the disk drive unit. The read/write heads associated with each platter fly above the platter surface on a cushion of air that is created by the air forces of the spinning platters. The heads ride very close to the platter surface so they can read and write magnetic information onto the platter surface. The characteristics of the air and the ski pads on the read/write heads dictate the attitude and movement of the flying read/write heads.
FIG. 1 illustrates a top view of a conventional disk drive system. The top surface of the top platter 10 is shown. The platters are spun by a spin motor. Each platter is centrally attached to the motor by the spin actuator 12. The arm assembly is shown as components 20, 22, 24 and 26. The arm assembly is also shown in FIG. 1 in two positions, an inner position "A" and an outer position "B". The arm assembly is made up of an actuator end 26 which is magnetically coupled for movement to pivot the assembly about pivot point 32. Pivot point 32 is coupled to the actuator arm section 20 which is also coupled to the head assembly 24 which holds the read/write head 22. The actuator end 26 is capable of moving the arm assembly from position A to B, thus the read/write head traverses the radius of the surface of platter 10. It is appreciated that the platter shown is but one platter in a parallel stack of platters. Another platter resides underneath the platter shown and another actuator arm, head assembly, and read/write head is associated with this platter. It is also appreciated that the bottom surface of platter 10 also bears information. Therefore, another actuator arm, head assembly, and read/write head is associated with the underside of platter 10. The entire system as described above is mounted to base 30.
The platters and actuator arm with associated heads are contained in a chamber within the disk drive unit. This chamber protects the platters and delicate movement required for the precise alignment of the platters to the actuator arm. Usually this chamber is sealed within a "clean room" having a reduced particle count so as to reduce the amount of dust and other particles that may become trapped especially between the platter and the read/write head within the drive case when the chamber is not sealed. These particles could render the disk drive inoperable if they were to become entrenched into the platters, read/write heads and other mechanisms.
Each read/write head associated with a platter of a disk drive is attached to a thin head assembly and an actuator arm. The head assemblies are manufactured and positioned so that each read/write head exerts pressure on a surface of the platter when assembled together and the disks are not in operation (i.e., spinning). The platters are aligned between each successive actuator arm, therefore one given actuator arm holds two read/writ heads and exerts pressure on a top surface of one platter but a bottom surface of another, adjacent, platter surface. The platter surfaces therefore exert pressure back on the actuator arm because the overall assembly remains static. For an actuator arm in between two platters, the forces exerted on the actuator arm from the platters are equal but in opposite direction and will balance each other to deliver a net zero force on the actuator arm. However, the actuator arms located on either end of the actuator assembly receive only one force exerted on them, either an upward or downward force depending on the side the actuator arm is located. In either case this force is outward, away from the actuator assembly. This imbalanced force, over time, may act to bring the actuator arm out of proper alignment and displace it outward.
In prior art disk drive systems, the top actuator arm receives an upward force from the head assembly which holds the top/read write head, but the top actuator arm receives no counter force from above since there are no platters above the top platter. This imbalance may act to bring the top actuator arm out of alignment or bend it away from its original position. Any movement out of alignment of the actuator arm will also move the read/write head out of its original path which will be fatal for the disk drive system and data failure and errors will result. In modern disk drive designs this problem becomes acute because the thickness of the actuator arms is decreasing as the disk drives become miniaturized. As the thickness of the actuator arms decreases the outer actuator arms become more susceptible to the force exerted by the associated read/write heads and therefore become more susceptible to movement out of alignment. It would be advantageous to be able to counter balance the outer actuator arms of disk drive actuator assemblies to prevent the failure condition described above in order to make the disk drives more reliable. The present invention offers such a solution.
In prior art systems the actuator arms are fairly thick, about 35 mils thickness. However, the present invention advantageously utilizes thin actuator arms, about 25 mils, which become very susceptible to these imbalanced forces from the flying read/write heads. The present invention utilizes thin actuator arms because the present invention operates in a reduced size hard disk drive where the components are advantageously reduced to conserve size and increase efficiency. The present invention offers a solution to the imbalanced forces using advantageously thin actuator arms and a force compensation apparatus and method.
The pressure exerted on the read/write heads by the head assembly (when the platters are at rest) is called the preload force. When the platters spin, an air bearing force lifts the read/write heads up off of the platter surface and they fly above the rotating surface. The preload force determines the height at which the read/write heads will fly. Any deviation of an outer actuator arm from its alignment position, as a result of the force imbalance of the above discussion, will change the preload value of the associated read/write head. This in turn changes the height at which the read/write head flies above the platter surface. If this height changes then data errors or a total failure will occur because the data on the disk platter is written in and read back by the read/write heads with respect to a predetermined flying height. In prior art systems any significant deviation of the outer actuator arms will cause the disk drive to fail. It would be advantageous to provide an arrangement that would maintain the alignment of the outer actuator arms so that the preload value of the associated read/write heads remains constant. This would then maintain the height of the read/write head above the platter surface when the disk drive was in operation. The present invention offers such a solution.
Therefore, it is an object of the present invention to maintain the alignment of the outer actuator arms of a disk drive by employing a compensation force on these outer arms that will maintain the preload force on the read/write heads associated with these outer arms. It is an object of the present invention to maintain the preload force on the read/write heads to maintain uniform flying height of the read/write heads above the platter surfaces. It is an object of the present invention to utilize the above alignment technique with actuator assemblies having thin actuator arms.